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Discussion Forum - Events - GPX's and Challenge Events


Author: Iain Connell
Posted: Mon 22nd Aug 2022, 10:11
Joined: 2010
Local Group: East Lancashire
Tony's point is well made regarding 'tracks' (recorded by GPS devices while on the move) and 'routes' (displayed by GPS devices in various ways including R/L turns, used for waypoint to waypoint navigation). Our downloadable LDPs GPX files are tracks (though can be converted into routes by some GPS devices and and websites), thus showing as a guide line on the maps displayed by GPS devices and now phone apps. Differences between 'as walked' and 'as mapped' GPX tracks is an indication of the accuracy of the 'as mapped' version, or how much you diverted from it, or both. Typically 'as walked' tracks will have wobbles and side-trips (guess what for), as well as errors and self-corrections, whereas 'as mapped' tracks may look like the lines in a guidebook.

Unfortunately it's not necessarily the case that 'as walked' tracks are more reliable, since they may include straight lines on 90deg corners (depending on the tracking settings permitted by the GPS device) and bends (including water-walking on canals), as well as 'dropouts' where satellite reception is lost (typically in ravines, between high buildings, and in woods). So a good 'as walked' GPX is one that's been edited, and as soon as possible after the walk. If you leave it too long, it's difficult to recall whether you short-cutted that bit because (a) you could (b) you had to (c) your GPS device 'straight-lined' it, or whether that side trip was (a) to avoid a bog which may not always be impassable (b) to avoid an obstacle which is likely to be there permanently (c) because you were simply off-route (or rather track) at that point. Frogspawn (multiple 'blob' clusters) are a feature of both minor errors (tacking about) and rest breaks (but maybe you sit down more than I do), which are easy to identify and edit out. Loops and backtracks are where you went wrong!
Author: Merrian Lancaster
Posted: Sat 20th Aug 2022, 18:47
Joined: 1996
Local Group: Beds, Bucks and Northants
I like "mapped gpx" and " walked gpx". They might not be technically accurate terms, but I understand them. And, I agree with the original post, please give us a "walked gpx", and, whatever is provided, please tell us if it's "walked" or "mapped".
Author: Andy Todd
Posted: Thu 18th Aug 2022, 12:26
Joined: 2010
Local Group: Wiltshire
Just because the file uses route/track/waypoint gives no assurance as to how it was created. A GPX file is just a text file, which can be edited in any text editor. Most gpx editors will allow you to save as either.

The important bit is how the data was generated, and that it has been checked. not that it is route or a track.

Below is a quick example gpx file, same thing, but as waypoints, track and route.


<?xml version="1.0"?>
<gpx version="1.1">
<name>example</name>
<wpt lat="50.73653" lon="0.23740">
<name>Start</name>
</wpt>
<wpt lat="50.73325" lon="0.23764">
<name>Finish</name>
</wpt>
<trk>
<name>track</name>
<trkseg>
<trkpt lat="50.73653" lon="0.23740" />
<trkpt lat="50.73325" lon="0.23764" />
</trkseg>
</trk>
<rte>
<name>route</name>
<rtept lat="50.73653" lon="0.23740" />
<rtept lat="50.73325" lon="0.23764" />
</rte>
</gpx>
Author: Tony Cartwright
Posted: Thu 18th Aug 2022, 9:18
Joined: 1978
Local Group: Surrey
Hi Andrew,

Thanks for your reply and your agreement with the general point I was trying to make - that of accuracy.

I do however take issue with you correcting me on the difference between a route and a track. My understanding is that a route is as envisaged or planned whilst a track is as walked. I think this is the generally held view. A 'GPX' per se may contain neither but just a collection of a few discreet and unconnected waypoints (eg checkpoint locations on an event or campsites on a walk).

Tony
Author: Andy Todd
Posted: Thu 18th Aug 2022, 6:38
Joined: 2010
Local Group: Wiltshire
Agree with your point, however your use of route and track is incorrect. The GPX needs to be one which has been captured on the ground (ground-truthed).

However, formatting a GPX as a track does not mean that it has been captured on the ground. Worth noting that tracks generally also contain time stamp data which you may want to remove, as well as other meta-data which you may want to remove.

As with all things in life, the GPX does need to be checked, You will often find errors in the recording which will need to be corrected.
Author: Tony Cartwright
Posted: Tue 16th Aug 2022, 14:58
Joined: 1978
Local Group: Surrey
Many Challenge Events are now providing a GPX of the route alongside the formal Route Description. If this is to be offered it's important that the GPX is a track and not a route, the difference being that a track is as walked on the ground against a route which is as planned/plotted from a map. A track will show the actual path walked and will thus accurately reflect the instructions in the RD. Any variance is at best annoying and at worst confusing - particularly when trying to reconcile the two in the dark.

Generating a track can be done at the same time as writing (or better when checking) the RD so it is really no great overhead, but the end result is that entrants have a GPX which pairs accurately with the RD.

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